A multi-SIM (subscriber identity module) wireless device, including particularly mobile devices such as mobile phones (including so-called “smart phones”), personal digital assistants, tablet and laptop computers, etc., can hold two or more SIM cards. Currently, such devices can typically hold two SIM cards, though phones that can hold three SIM cards are now available and it is likely that phones and other wireless devices that can hold more SIM cards will become available. It is mentioned here that there are proposals to replace SIM cards with SIM functionality provided by software in the device. Reference will be made in this specification generally to “SIM” to mean that part of a device that provides for the subscriber identity module functionality whether provided by a physical card, software elsewhere in the device, or any other suitable arrangement. In addition, for simplicity and brevity, reference will often be made in this specification to a dual-SIM device, which can operate with two networks and/or tariff arrangements, etc., but it will be understood that much of what is described herein can be applied to a multi SIM wireless device having in principle any number of SIMs for operating with a corresponding number of networks and/or tariff arrangements, etc.
Dual-SIM operation allows the use of two services without the need to carry two devices at the same time. For example, the same handset can be used for business and private use with separate numbers and bills. As another example, the same handset can be used for travel, with one SIM being for use in the home country and the other SIM being for the country visited. As another example, both SIMs may be used with the same network operator, for example to achieve a higher total bandwidth for data connections. As yet another example, the device may contain both cellular and non-cellular radios which are used for voice and data communication respectively using the different SIMs. In any event, using multiple SIMs allows the user to take advantage of different pricing plans for calls and text messages to certain destinations as well as mobile data usage, and/or to keep personal and business use separate for example, and/or to achieve higher bandwidth, and/or to obtain coverage across different networks using a single handset. With this multiple SIM functionality, the SIMs can in general be from any network operator. The embodiments described herein are particularly concerned with mobile wireless devices that have two (or more) SIMs and radio systems which can be used simultaneously, and thus allow for example a user to send or receive data whilst making a voice call, and/or to have plural voice calls active simultaneously, and/or to have plural data calls active simultaneously, all on the one device and using the separate radio systems.
It can be expected that in practice, one of the two SIMs in these examples will spend a significant amount of time out of suitable service. Suitable service is allowed service on the home network, an equivalent network or an allowed roaming network. The typical states for the SIM in such a case are performing searches to return to suitable service and/or camping on an acceptable network to at least provide emergency service. However, even in these states, considerable power is consumed by the SIM channel, particularly by the receiver components (which in general will include the antenna(s), radio frequency system, processor system, etc. servicing the SIM channel for that SIM). It may be noted here that these states are often called “idle” states even though the SIM channel is consuming power. A particular problem with a dual (or more) SIM device is the high level of power consumed by the device, particularly for those that duplicate the radio hardware, software, firmware, etc.